Beat sugar and eggs together in a mixing bowl. Beat in the flour. Bring1-1/2 cups of heavy cream to a simmer in a saucepan. Slowly beat the hot cream into the bowl of egg and sugar mixture. Pour the entire mixture back into the sauce over low heat. Stir constantly with a whisk or wooden spoon until the custard thickens.
Be careful not to let the mixture boil or the eggs will scramble. Remove from the heat and pour in the remaining heavy cream and the soy sauce into a sealable bowl, whisking to combine. Cover and freeze until ready to use.